Fuse structures with striker pins



P 1956 F. J. KOZACKA ETAL 2,761,932

FUSE STRUCTURES WITH STRIKER PINS Filed April 6, 1955 740711111 VIII/nilUnited States Patent FUSE STRUCTURES WITH SIRIKER PINS Frederick J.Kozacka, Southampton, and Kenneth W.

Swain, Hampton Falls, N. H., assignors to The Chase- Shawmut Company,Newburyport, Mass.

Application April 6, 1955, Serial No. 499,651

'12 Claims. (Cl. 200-117) This invention relates to fuses, and moreparticularly to fuses of the current-limiting type.

The properties of the material of which the casing of a fuse is madehave important effects upon the performance characteristics of the fuse.Among the various materials which have been tried for making the casingsof currentlirniting fuses synthetic-resin-glass-cloth laminates provedto be particularly desirable because they combine high bursting strengthwith other desirable properties, such as high resistance to heat shock,minimum tracking, etc.

It is one object of this invention to provide very compact fusestructures having casings of synthetic-resin-glass-cloth laminates, and/or particularly adapted for this type of casing material.

In a series of tests which we conducted with prior art current-limitingfuses having casings made of syntheticresin-glass-cloth laminates wefound upon decreasing the size of the casings and increasing the wallthickness and bursting strength thereof that there was a tendency towardfailure due to mechanical breakdowns at the terminal elements of thefuses.

Decreasing the size or internal volume of the casings resulted in anincrease of internal pressure incident to blowing of the fuses whichincrease was compensated for by the increase in bursting strength of thecasings. As a result, the casings of the prior art fuses of decreasedsize remained intact even under very severe interrupting conditions. Theterminal elements of the fuses having become the points of leastmechanical strength, failures tended to occur at these points.

It is another object of this invention to provide improved fusestructures wherein high bursting strength of the terminal elements isachieved concomitant with great compactness and small weight, andwherein the leakage of hot products of arcing to the space outside ofthe casings is eliminated, or minimized.

Still another object of the invention is to provide improved fusestructures wherein the casing closing parts of the terminal elements andthe conductors for carrying current to and from the casing closing partsare firmly clamped together in abutting relation combining greatmechanical strength of the joint and small contact resistance thereof.

Another object of the invention is to provide improved fuse structureshaving mechanically strong relatively light terminal elementsparticularly adapted to be, and being, conductively interconnected bytubular high-current-carrying-capacity fuse links.

Still another object of the invention is to provide fuse structurescomprising improved so-called striker pins, i. e. parts acted upon by aconsiderable force released upon blowing of the fuse to trip a circuitbreaker, or to perform an equivalent mechanical task.

The novel features that are characteristic of the invention are setforth in particular in the appended claims. The invention itself,however, both as to structure and operation together with additionalobjects and advan-,

tages thereof will best be understood from the following "ice detaileddescription of a preferred embodiment thereof when read in connectionwith the accompanying drawing in which,

Fig. l is substantailly a longitudinal or axial section of a fuseembodying our invention, a portion of the fuse link and of the casingbeing shown in front view;

Fig. 2 is a side elevation of the structure shown in Fig. I seen in thedirection of the arrow R1; and

Fig. 3 is a side elevation of the structure shown in Fig. I seen indirection of the arrow R2.

Referring now to the drawing, reference character a has been applied toindicate a tubular casing of insulating material, preferably asynthetic-resin-glass-cloth laminate, Either silicones or other suitablesynthetic resins may be used to form the tubular glass-cloth laminate ofwhich casing a consists. A pair of terminal caps b is inserted intocasing a in such a way that each protrudes with the bottom end thereofinto casing a and projects with the opposite end thereof outside ofcasing a. Each cap b comprises a relatively thick and rigid bottomportion d and a relatively thin resilient lateral wall portion.Reference character 0 designates a shoulder formed between the twoaforementioned portions of terminal caps b. The bottom portion d of eachcap b defines a cylindrical surface having a smaller diameter than theinternal diameter of casing a. The multiperforated tubular fuse link eis supported by, or mounted on, the small diameter bottom portion ofcaps b. The required contact pressure between caps b and tubular fuselink e is established by a pair of inner split rings 1 upon each ofwhich a non-split ring 3 is pressure-mounted. If desired, soldering maybe substituted for this type of pressure connection between caps b andlinke e. Link e consists preferably of silver. As an alternative,tubular links of copper may be used. Other than these low resistivity,low fusing energy metals are not particularly suitable for formingtubular link e. The inside of casing a is filled with a siliciousarc-quenching filler t such as chemically fairly pure quartz sand. Theportion of each cap b situated outside of easing a forms a shoulder uand each of a pair of substantially circular plates h rests against oneof the two shoulders u. The two shoulder surfaces u are substantially atright angles to the longitudinal axis of easing a and form substantiallycircular contact surfaces for the plates h. Contact surfaces u are onlyengaged by the outer periphery of plates h, and plates h are firmlyclamped against contact surfaces u by a substantially circular bend ofabout degrees of the axially outer ends of caps a. Each plate h isprovided with a substantially radial extension or tab hi. Extensions ortabs h1 project through gaps w of limited width interrupting thecircumference of the circular edges of caps b situated outside of casing(1. These edges are being bent down upon, and rolled against, the outersurfaces of plates h, whereby plates 12 are tightly locked betweensurfaces u on caps b and the bent and rolled edges of caps b. Theextension or tab hr of left plate h is bent 90 around casing a andprovided with a plug contact k adapted to cooperate with a suitablehollow contact (not shown), generally known as a tulip-type contact. Theextension or tab hr of right plate 11 is likewise provided with a plugcontact k adapted to cooperate with a suitable hollow contact (notshown). The 90 degree bend in extension or tab hl of left plate henables to space plug contacts k a shorter distance than the length ofcasing a, which is conducive to great compactness. Terminal caps 12 aresecured to casing a by a plurality of angularly displaced rivets lhavingupset heads on both ends of the shanks thereof or, in other words,standard rivets as distinguished from special rivets for blind riveting.

The bottom end of right cap b is provided with a relatively narrowcentral aperture x1 and the bottom end of left cap b is provided with arelatively wide central aperture x2. Wire-type fuse link r is made of amaterial having a relatively high tensile strength such as, for in:stance, steel wire. "It is arranged substantially in the center of, orcoaxially with, casing a and tubular fuse link e and conductivelyinterconnects both terminal caps b. To this end the left end ofwire-type fuse link r is inserted into aperture in into which wedgeelement s is being driven for firmly wedging fuse link r therein. Theother or right end of fuse link r is threaded through two washers m andn and firmly secured to a plunger p known as striker pin projectingthrough center hole z' in the right plate 11. There are severaldifferent ways in which link r may be secured to plunger p as, forinstance, by Wedging or soldering. Soldering has been found to be adesirable mode of connecting parts r and p, provided that wire 1' is notyery thin. For very thin wires r'a wedge type connection between who rand plunger p such as shown in Fig. 1 is preferable. Wire r is insertedinto a pair of bores p1 in plunger 2 arranged at right angles and heldtherein by wedge pin p2. Helical spring rests with one end againstwasher 21 consisting of a relatively hard material such as, forinstance, fiber and with the other end against a collar on plunger 11and thus biases plunger p from left to right, as seen in Fig. l. Washerm consists of a relatively soft material such as an elastomer. Sincerelatively high temperatures may be encountered at the point wherewasher m is located, the material of which washer m is made ought to beheat resistant. In view of these conditions Washer 111 should preferablybe made of a soft silicone rubber.

When assembling the fuse structure, first a subassembly is madecomprising link wire r and plunger p firmly attached to one end of linkwire r. Thereupon link wire 1' is threaded through washers n and m,narrow hole x1, tubular fuse link e and wide hole x2, and Wedge s isbeing driven into hole x2 while link wire r is being held taut.

It appears from the foregoing that the Way in which link wire 1' issecured to plunger p is optional but that it is essential that it besecured by wedge action to the left terminal cap b.

When the fuse is connected into an electric circuit link Wire r isshunted by tubular fuse link e, and the amount of current then carriedby link wire r is negligible. The current path through link wire r is asfollows: part a! of left cap 12, wedge element s, wire r, plunger p,helical spring 0, part 0. of right cap b. A few turns of helical spring0 are inserted into a recess in part d of right cap b accommodating thetwo washers m and n. These turns are in frictional engagement with partd of right cap b and conduct current from plunger p to part it of rightcap b.

Washer 11 upon which helical spring p rests compresses washer m made ofan elastomer, as a result of which Washer 111 establishes a gastightseal between the arcing chamber of the fuse, i. e. the space withinwhich tubular link e is situated, and the space outside of said chamber.

'In the process of assembling the fuse, before riveting the terminalcaps b to casing a and securing circular plates 12 to caps b, anexpandible mandrel may be inserted into thelatter to produce a closepressed fit between caps b and casing a.

If desired, the spaces or chambers formed between bottom parts d of capsb and plates h maybe adaptedto receive limited quantities of products ofarcing allowed to leak from the aforementioned arcing chamber into thesespaces. Controlled leakage of are products may provide some pressurerelief within the arcing chamber without resulting in the slightestemission of hot gases from the fuse structure to the outside.

On occurrence of major fault currents series breaks are formed'by fusionof tubular fuse link 6. As the resistance of the gaseous arc-path takingthe place of fuse link e increases with progressive cooling thereof,wire link r is caused to carry current and to fuse. Thus plunger p is nolonger restrained by wire link r and spring o is in a position to pushplunger p from left to right until the collar on plunger p abuts againstthe inside of the right plate 11.

A particular advantage of the construction shown consists in that thearea of contact between plates h and caps b is relatively large and inthat the current density is not particularly high at any point of thestructure, except the necks of the fuse link e, where the currentdensity ought to be high.

It will be understood that we have illustrated and described a preferredembodiment of our invention and that various alterations may be made inthe details thereof without departing from the invention as defined inthe appended claims.

We claim:

1. A fuse comprising in combination a tubular casing of insulatingmaterial, fuse link means within said casing, a pair of terminal capsinserted into said casing and conductively interconnected by said fuselink means, each of said pair of caps protruding with the bottom endthereof into said casing and projecting with the opposite end thereofoutside of said casing, a portion of each of said pair of caps forming acontact surface at substantially right angles to the longitudinal axisof said casing, a substantially circular pair of plates each abuttingwith the outer periphery thereof against said contact surface on one ofsaid pair of caps and each clamped against said contact surface by abend on one of said pair of caps.

2. A fuse comprising in combination a tubular casing of insulatingmaterial, fuse link means within said casing, casing closing means onboth ends of said casing conductively interconnected by said fuse linkmeans, said closing means including a terminal cap protruding with thebottom end thereof into said casing and projecting with the opposite endthereof outside of said casing, a portion of said cap defining a contactsurface at substantially right angles to the longitudinal axis of saidcasing, and a substantially circular plate engaging said contact surfacewith the outer periphery thereof and clamped against said contactsurface by a bend on said cap.

3. A fuse comprising in combination a tubular casing of insulatingmaterial, fuse link means within said casing, closingmeans on both endsof said casing conductively interconnected by said fuse link means, saidclosing means including a terminal cap protruding with the bottom endthereof into said casing and projecting with the opposite end thereofoutside said casing, a portion of said cap forming a contact surface atsubstantially right angles to the longitudinal axis of said casing, asubstantially circular plate engaging said contact surface and clampedagainst said contact surface by a bent portion on said cap, an aperturein said plate, a plunger arranged in the space between said bottom endof said cap and said plate projecting through said aperture, a springresting against said bottom end of said cap biasing said plunger to moveWithin said aperture, and fusible restraining means for said plungerreleasing said plunger upon fusion of said fuse link means.

4. A fuse comprising in combination a tubular casing of insulatingmaterial, fuse link means within said casing, a pair of terminal capsarranged within and riveted to said casing and conductivelyinterconnected by said fuse link means, each of said pair of capsprotruding with the, bottom end thereof into said casing and projectingwith the opposite end thereof outside of said casing, a shoulder definedby said opposite end of each said pair of caps, and a substantiallycircular pair of plates each engaging said shoulder on one of said pairof caps and clamped against said shoulder by a bent portion on each ofsaid pair of caps.

5. A fuse comprising in combination a tubular casing of insulatingmaterial, a ribbon-type fuse link having a relatively highcurrent-carrying capacity arranged within said casing a wire-ty pe fuselink having a relatively small curren -ca in ten it a r n ed h n s deein a plunger attached to one end of said wire-type fuse link, a springbiasing said wire-type fuse link and said plunger in a directionlongitudinally of said casing, closing means on both ends of said casingconductively interconnected by said ribbon-type fuse link and by saidwire type fuse link, said closing means including a terminal capprotruding with the bottom end thereof into said casing and projectingwith the opposite end thereof outside of said casing, 21 substantiallycircular shoulder defined by said opposite end of said cap, asubstantially circular plate having an aperture in the center thereofengaged by said plunger, said plate resting against said shoulder ofsaid cap and being clamped against said shoulder by a substantiallycircular bent portion on said opposite end of said cap overlapping theperiphery of said plate.

6. A fuse comprising in combination a tubular casing of insulatingmaterial, a fuse link within said casing, a pair of terminal capsinserted into and riveted to said casing conductively interconnected bysaid fuse link, said pair of caps protruding with the bottom endsthereof into said casing and projecting with the opposite ends thereofoutside of said casing, substantiallycircular shoulder portions on theinner surfaces of said pair of caps, and contact means for insertion ofthe fuse into a fuse holder including a pair of substantially circularplates resting against said shoulder portions and held in position bybends of about 90 degrees of the lateral sides of said pair of capsoverlapping said pair of plates.

7. A current-limiting fuse comprising in combination a tubular casing ofa synthetic-resin-glass-cloth laminate, a fuse link of ahigh-conductivity low fusing energy metal within said casing, apulverulent silicious arc-quenching filler surrounding said fuse link, apair of terminal caps conductively interconnected by said fuse linkriveted to said casing, said pair of caps having substantially closedends protruding into said casing and substantially circular edgeportions situated outside of said casing, each of said edge portionshaving a gap in the circumference thereof, said pair of caps furtherhaving substantially circular shoulder portions coaxial with said edgeportions, and contact means associated with said pair of caps, saidcontact means including a pair of substantially circular plates eachhaving a substantially radial extension, said pair of plates abuttingagainst said shoulder portions on said pair of caps and each projectingwith the radial extension thereof through said gap, said pair of platesbeing held in position by said edge portions on said pair of caps bentaround about 90 degrees to overlap said pair of plates.

8. A current-limiting fuse comprising in combination a tubular casing ofa synthetic-resin-glass-cloth laminate, substantially tubular fuse linkmeans coaxially arranged within said casing, a pair of terminal capseach comprising a relatively thick and rigid bottom portion and arelatively thin and resilient lateral wall portion, said bottom portionof each said pair of caps including a cylindrical surface having asmaller diameter than the internal diameter of said casing andsupporting said fuse link, said lateral wall portion of each of saidpair of caps having an outer diameter substantially equal to the innerdiameter of said casing and supporting said casing, and a plurality ofrivets upset on both ends of the shanks thereof extending transverselyacross said casing and said lateral wall portion of each of said pair ofcaps.

9. In a fuse the combination of a tubular casing of insulating material,a ribbon-type fuse link having a relatively high current-carryingcapacity arranged within said casing, a wire-type fuse link having arelatively small current-carrying capacity arranged within said casing,21 pair of terminal elements conductively interconnected by saidribbon-type fuse link closing the ends of said casing, one of said pairof terminal elements having a relatively narrow central aperture and theother of said pair of terminal elements having a relatively wide centralaperture, one end of said wire-type fuse link being threaded throughsaid relatively narrow aperture, a spring-biased plunger attached tosaid one end of said wire-type fuse link, the other end of saidwire-type fuse link being inserted into said relatively wide aperture,and a wedge element driven into said relatively Wide aperture for firmlywedging said other end of said wire-type fuse link therein.

10. A fuse comprising in combination a tubular casing of insulatingmaterial, a ribbon-type fuse link having a relatively highcurrent-carrying capacity arranged within said casing, a wire-type fuselink having a relatively small current-carrying capacity arranged withinsaid casing, a pair of terminal elements on said casing conductivelyinterconnected by said ribbon-type fuse link and by said wire-type fuselink, an aperture in one of said pair of terminal elements, a firstwasher of an elastomer having an aperture and arranged adjacent said oneof said pair of terminal elements, a second Washer of a relatively hardmaterial having an aperture and arranged in abutting relation to saidfirst washer, a plunger, one end of said wire-type fuse link beingthreaded through said aperture in said one of said pair of terminalelements, through said aperture in said first washer and through saidaperture in said second washer and attached to said plunger, and ahelical spring arranged in abutting relation to said plunger and to saidsecond washer to compress said first washer and to move said plungerupon fusion of said Wire-type fuse link.

11. A fuse comprising in combination a tubular casing of insulatingmaterial, a substantially tubular fuse link of sheet metal arrangedsubstantially coaxially within said casing, a wire-type fuse linkarranged substantially coaxially within said tubular fuse link, a pairof terminal caps inserted into said casing and conductivelyinterconnected by said tubular fuse link and by said wire-type fuselink, each of said pair of caps protruding with the bottom end thereofinto said casing, a plurality of angularly displaced rivets havingshanks upset on both ends thereof securing said pair of caps to saidcasing, one of said pair of caps having a relatively narrow centralaperture and the other of said pair of caps having a relatively widecentral aperture, a first washer of an elastomer having a relativelynarrow central aperture and arranged immediately adjacent to said one ofsaid pair of caps, a second washer of a relatively hard material havinga relatively narrow central aperture and arranged in abutting relationto said first washer, a plunger, one end of said wire-type fuse linkbeing threaded through said aperture in said one of said pair of caps,through said aperture in said first washer and through said aperture insaid second washer and attached to said plunger, a spring arranged inabutting relation to said plunger and to said second washer tending tostress said wire-type fuse link, and a Wedge element driven into saidrelatively wide aperture on said other of said pair of caps for securingtherein the other end of said wiretype fuse link against the action ofsaid spring.

12. A fuse comprising in combination a tubular casing of insulatingmaterial, a ribbon-type fuse link and a wire-type fuse link botharranged within said casing, a pair of terminal caps inserted into saidcasing and conductively interconnected by both said fuse links, each ofsaid pair of caps protruding with the bottom end thereof into saidcasing and projecting with the opposite end thereof outside of saidcasing, a contact surface at substantially right angles to thelongitudinal axis of said casing formed by a portion of each of saidpair of caps, a substantially circular pair of plates each abutting withthe outer periphery thereof against said contact surface on one of saidpair of caps and each clamped against said contact surface by a bendformed on said opposite end on each said pair of caps, one of said pairof plates having an aperture in the center region thereof, a plungernormally restrained in position by said wire- 7 y y se lin slida ly apanged ithig said ap ure and a. spring accommodated ir lthe space boundedby said 9116' o fsz ai d pair of plateg and By one 0f s ai d pai; of

C ;1-P$ iimndjzitcly ad acent threto bia sing said plunger akilly bii twardly of said casing.

References Cited in the file of this patent UNITED STATES PATENTS1,046,705 Young Dec. 10, 1912 Great Britain Apr. 7, 1932

